Alphabet Rotation Pattern (Cyclic Wrap-Around Rows) in JavaScript

What You’ll Learn

Each row is a fixed width of rows letters, but the start letter shifts forward every line: ABCDE, BCDEA, CDEBA, DECBA, EDCBA for five rows. Two inner loops per row - forward to the top letter, then wrap down to A - teach cyclic rotation without string tricks. Compare with Program 1 (growing rows, no wrap). Includes a live preview, worked JavaScript examples, edge cases, and complexity.

📝 Problem & Approach

Given a positive integer rows, print rows lines of exactly rows uppercase letters each. Row 1 starts at A and runs forward to the top letter; each next row starts one letter later and wraps back to A after the top.

// First 5 rows
// ABCDE
// BCDEA
// CDEBA
// DECBA
// EDCBA

Inputs & Outputs

Minimal workflow

base = "A".charCodeAt(0)
top = base + rows - 1
for i from base to top:
    line = ""
    append letters i..top (forward)
    append letters (i-1)..base (wrap, descending)
    console.log(line)

Approach comparison

🔮 Live Preview

Choose a row count between 1 and 26 and draw the alphabet rotation pattern in the browser.

Press "Draw pattern".

Examples Gallery

Three complete JavaScript programs - fixed five rows with two inner loops, prompt input, and a slice rotation shortcut. Click View Output to reveal sample console results, or Try it Yourself to run in the browser editor.

let rows = 5;
rows = Math.max(1, Math.min(rows, 26));

const base = "A".charCodeAt(0);
const top = base + rows - 1;

for (let i = base; i <= top; i++) {          // A..E
  let line = "";
  for (let j = i; j <= top; j++) {         // i..E (increasing)
    line += String.fromCharCode(j);
  }
  for (let k = i - 1; k >= base; k--) {    // (i-1)..A (decreasing)
    line += String.fromCharCode(k);
  }
  console.log(line);
}

ABCDE
BCDEA
CDEBA
DECBA
EDCBA

let rows = parseInt(prompt("Enter number of rows (1-26):"), 10);
if (!Number.isFinite(rows)) {
  console.log("Please enter a whole number.");
} else {
  rows = Math.max(1, Math.min(rows, 26));

  const base = "A".charCodeAt(0);
  const top = base + rows - 1;

  for (let i = base; i <= top; i++) {
    let line = "";
    for (let j = i; j <= top; j++) {
      line += String.fromCharCode(j);
    }
    for (let k = i - 1; k >= base; k--) {
      line += String.fromCharCode(k);
    }
    console.log(line);
  }
}

Enter number of rows (1-26): 3
ABC
BCA
CBA

let rows = 5;
rows = Math.max(1, Math.min(rows, 26));
const letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".slice(0, rows);

for (let i = 0; i < rows; i++) {
  console.log(letters.slice(i) + [...letters.slice(0, i)].reverse().join(""));
}

ABCDE
BCDEA
CDEBA
DECBA
EDCBA

🔎 Worked Walkthrough — rows = 5

Trace each outer-loop value of i and see how the forward and wrap parts combine into each printed row.

Total character prints: 5 × 5 = 25 = n² for n = 5 rows.

🎯 Practice Problems

Try these variations to lock in the pattern.

Notes

⏱️ Time and Space Complexity

💡 Best Practices